If we separate the constituents of the heterogeneous system, we would be carrying out a process of phase separation. See below the procedures by which these phases can be isolated:
Separation methods for heterogeneous systems
Sublimation: allows isolating substances that sublime and vaporize from those that do not. For example, it is possible to separate sand from iodine.
Levigation: allows separating lighter solids from heavier ones. For example, separating rock pieces from sand. This procedure is carried out by currents of water that drag the light particles.
Decantation: is the process by which a solid is separated from a liquid or two immiscible liquids (such as water and oil), by different density.
Centrifugation: allows accelerating the decantation process by means of centrifugal force (circular motion). Decantation will be faster as the number of turns in a given period of time increases.
Extraction: consists of separating one of the components of a mixture by dissolving it with the appropriate solvent. For example, to extract the green pigment from a leaf, it is boiled in a water bath with alcohol for a few minutes.
Another example of phase separation using the extraction method is in the preparation of tea or coffee infusion, extracting from the leaves or beans substances that give the characteristic aroma and flavor.
Solubilization: is the process by which a solid is separated from another by dissolving one of the phases in water. For example, the sugar-sand system.
Filtration: using this procedure, it is also possible to separate a solid phase from a liquid one (such as the water-sand system).
Sieving: is the process by which solids such as sand and rocks are separated, taking advantage of their different volume.
Separation methods for homogeneous systems
Homogeneous systems can be fractionated when they are not pure substances. The methods are as follows:
Distillation: in a homogeneous system of water and alcohol, the difference in boiling points can be used to separate them. It consists of evaporating one of the liquids and then condensing it by cooling. If the boiling points are close, fractional distillation is used, different from simple distillation, used if they are distant points.
There are two main types of distillation: simple distillation and fractional distillation.
- Simple distillation is used to separate two liquids with different boiling points. The liquid mixture is heated until it boils, and the vapor rises and is collected in a condenser. The condenser cools the vapor, which turns back into a liquid and is collected in a separate container. This method works well when the boiling points of the two liquids are far apart.
- Fractional distillation is used when the boiling points of the two liquids are closer together. In this method, the liquid mixture is heated and the vapor is passed through a column that is packed with a material, such as glass beads or metal mesh, which provides a large surface area for the vapor to condense. As the vapor rises up the column, it cools and condenses, and the liquids with lower boiling points will condense first. The fractions with different boiling points are then collected separately.
Both types of distillation are commonly used in chemistry and industry for separation and purification of liquids.
Crystallization: isolates solids that crystallize from the solution in which they are dissolved. Saltwater is an example. When heated, water evaporates and salt crystals remain. It is a reverse process to dissolution, which is frequently used for substance purification in industry, such as obtaining table salt.
Other separation methods
there are other separation methods in addition to the ones mentioned. Here are some additional separation methods:
- Chromatography: This is a technique used to separate and identify the components of a mixture. It involves passing the mixture through a stationary phase, such as a column packed with a solid material, and a mobile phase, such as a liquid or gas that moves through the stationary phase. Different components will move through the stationary phase at different rates and can be collected and analyzed separately.
- Electrolysis: This is a process that uses an electrical current to drive a chemical reaction. It can be used to separate mixtures of compounds that can be ionized, such as ionic compounds dissolved in water. The current causes the ions to move toward electrodes of opposite charges, where they can be collected separately.
- Precipitation: This method involves adding a chemical to a mixture that causes one or more components to form a solid precipitate that can be separated from the remaining liquid.
- Magnetization: This method involves using magnets to separate magnetic materials, such as iron or steel, from non-magnetic materials, such as sand or gravel.
- Crystallization by evaporation: This is a process where a solution is allowed to evaporate slowly, causing the dissolved solute to form crystals that can be collected and separated from the remaining liquid.
- Membrane filtration: This is a method of separating particles or molecules of different sizes using a membrane with specific pore sizes. The smaller particles or molecules will pass through the membrane, while the larger ones will be retained and can be collected separately.
These are just a few examples of other separation methods. The choice of method will depend on the specific properties of the mixture and the components that need to be separated.
Summary of Separation Methods
| Separation Method | What it is used for |
|---|---|
| Centrifugation | Separating solids from liquids by spinning them rapidly around a central axis. Used to separate mixtures of substances with different densities, such as blood cells from plasma. |
| Levigation | Separating heavier particles from lighter particles by shaking them in water. Used to separate sand from gravel, for example. |
| Decantation | Separating a liquid from a solid by pouring the liquid off the top. Used to separate oil and water, for example. |
| Extraction | Separating a specific substance from a mixture using a solvent. Used to extract caffeine from coffee beans or essential oils from plants. |
| Sieving | Separating small solid particles from larger ones using a mesh screen. Used to separate flour from lumps or to remove pebbles from sand. |
| Evaporation | Separating a liquid from a solid by heating it to turn the liquid into a gas, leaving the solid behind. Used to separate salt from water, for example. |
| Chromatography | Separating a mixture of substances based on their different chemical properties. Used to identify and isolate specific compounds in a mixture, such as different pigments in ink. |
| Distillation | Separating a mixture of liquids based on their different boiling points. Used to separate alcohol from water in distillation of spirits or to purify water. |
| Filtration | Separating solid particles from a liquid or gas by passing it through a filter. Used to remove impurities from water, for example. |
| Crystallization | Separating a solid from a liquid by cooling the solution, causing the solid to form crystals. Used to purify substances such as salt or sugar. |
Activities:
1. Indicate the method or methods you would use to separate…
- …a system made up of vinegar, water, and oil.
- …the system of lemon juice-lemon pulp.
- …the salt-water-coal dust system.
- …the system of rocks-gold nuggets-river water.
2. What is the difference between filtration and decantation, and when would you use one method over the other?
3. How does centrifugation work, and what type of mixtures is it typically used for?
4. What is distillation, and how is it used to separate a mixture of liquids with different boiling points?
5. How does chromatography work, and what types of mixtures is it commonly used to separate?
6. Explain the process of magnetization, and give an example of a mixture that can be separated using this method.
Teaching resources
There are several online sources where you can find simulations or virtual labs for separating methods of mixtures. Here are a few examples:
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PhET Simulations – This website provides a variety of interactive simulations for science and math topics, including simulations for separating mixtures. They offer simulations for chromatography, distillation, and more. You can access their simulations for free at https://phet.colorado.edu/en/simulations/category/chemistry.
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Virtual Chemistry Lab – This website provides a virtual lab for separation methods that allows you to perform experiments using a variety of separation techniques, including filtration, decantation, and distillation. You can access the virtual lab for free at http://www.virtual-chemistry-lab.com/separation-of-mixtures.html.
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ChemCollective – This website offers a range of interactive activities and simulations for chemistry topics, including separating mixtures. They offer simulations for distillation, chromatography, and more. You can access their resources for free at http://chemcollective.org/vlabs.
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Labster – This is a virtual lab platform that offers a range of simulations for science topics, including chemistry. They offer virtual labs for separation methods such as chromatography, filtration, and more. You can access their resources through a subscription at https://www.labster.com/.
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CK-12 – This website offers a variety of interactive activities and simulations for science and math topics, including separating mixtures. They offer simulations for distillation, filtration, and more. You can access their resources for free at https://www.ck12.org/student/.
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